Method for producing nonslip floor coverings

ABSTRACT

The invention relates to a method of manufacturing non-slip floor coverings made of mineral materials, such as, for example, natural stone, fine stoneware, artificial stone or ceramics. This method is carried out in a two-stage process, there being produced on the surface of the floor coverings or slabs, in a first process stage by means of pulsed laser bombardment, statistically distributed microcraters invisible to the human eye. The surface of the floor coverings or slabs obtained in this way is then, according to the invention, subjected to hydromechanical aftertreatment.

BACKGROUND OF THE INVENTION

The invention relates to a method of manufacturing non-slip floorcoverings made of mineral materials, such as, for example, naturalstone, fine stoneware, artificial stone or ceramics.

A special area of application for the invention is to increase orproduce an anti-slip effect on highly polished floors, especially thoseused in public buildings or in buildings accessible to the public, aswell as in those areas where liquids of every kind can land on thefloor.

Slipping is one of the most frequent causes of accidents in Germany. Theseverity of such accidents is usually underestimated. To increase safetyunderfoot, shoe-soles and floors must be designed to be anti-slip. Thisis necessary above all where media which encourage slipping land on thefloor. In many areas of public life, but also in the private domain, itis usual to use polished, shiny natural stone and artificial stone slabsas typical floor coverings both in dry and wet areas and in transitionalareas. What is important here is to bring the anti-slip characteristicsinto harmony with the architectonic aesthetics. The evaluation of theanti-slip effect takes place according to DIN 51097—(Determining theanti-slip property—barefoot regions subject to wetness—inspectionprocedures—inclined plane) and DIN 51130 (Determining the anti-slipproperty—workrooms and work areas with increased danger ofslipping—inspection procedures—inclined plane) by means of an inclinedplane.

However, there also exist measuring implements for the non-stationarymeasurement of the coefficient of friction. [Fb 701 Comparative study ofthe non-stationary measurement of the coefficient of friction on floors(Schriftenreihe der Bundesanstalt für Arbeitschutz)].

There exist different methods of producing or increasing the anti-slipproperties of floors made of natural or artificial stone. The use ofthese methods is predominantly dependent on where the floor covering isto be laid or is already laid (inside area, outside area, degree ofsoiling to be expected, amongst other things). The most importantmethods will be briefly described below.

In abrasive blasting, abrasive-blasting materials corresponding to thedesired roughness are hurled against the surface at high pressure. Themore or less hard abrasive-blasting material leads to irregularroughening and severe dulling of the surface (DE 31 39 427).

In flame-blasting, high-energy fuel-gas oxygen flames are produced withwhich the surface to be treated is briefly heated. Through the action ofthe flames, there is a bursting of the quartz in the uppermost region ofthe stone as well as melting of stone portions which then solidify likeglass and adhere to the surface relatively loosely (DE 35 45 064).

The granulation takes place with the use of a granulating tool(granulating hammer) which is provided with a plurality of evenlyarranged chisel points. During a continuous movement of the workpiece,the granulating hammer is struck against the surface with a certainfrequency (DE 39 33 843).

The described, or similar, methods which use abrasive means orchisel-like tools, admittedly lead to an increase in safety underfoot,but, like other surfaces, for instance those which are less polishedduring manufacture, also to a considerable loss of brightness and thus areduction in their aesthetic appeal.

The coating of surfaces in order to increase their non-slip quality hasthe consequence that the treated surface is provided with burls (DE 3342 266). This method does not admittedly bring with it any alteration ofthe visual characteristics but is only of limited durability since it isnot possible to avoid abrasion.

In the chemical etching treatment of natural stone surfaces, above allthe feldspar portions are attacked by the effect of substancescontaining hydrofluoric acid. (Informationsblatt des BundesverbandesTrittsicherheit, Abteilung Öffentlichkeitsarbeit). The damage onlyamounts to a few micrometers, the quartz is largely spared. The loss ofbrightness depends on the length of the action; the alteration of thewhole appearance must be tested on a sample surface.

However, this method is largely limited to being applied to mineralfloor coverings. Chemical composition and concentration must be adaptedto the different types of coverings. Because of the long reaction timesand the necessity of keeping to the exact concentration, this methodcannot be integrated into the process of manufacturing floor slabs orflags, or only with very high outlay. Where there is inappropriateapplication and disposal of the substance containing hydrofluoric acid,there is an increased risk to workers' safety and the conservation ofthe environment.

In DE 195 18 270 or WO 96/36469, a non-slip floor covering and a methodof manufacturing same are likewise described, the anti-slip effect beingachieved here in that a dense net of microcraters, which are supposed tobe invisible to the human eye, is produced on the surface of the floorcovering, preferably polished slabs of natural stone or fine stoneware,by means of laser irradiation. This solution represents a clearimprovement on the preceding state of the art.

An increase in the anti-slip effect, however, such as is desirable, e.g.in certain wet areas, can admittedly be achieved with laser irradiationby increasing the density of the craters and enlarging the lateralextension and the depth of the craters.

What is disadvantageous here, however, is that there can then be clearimpairment of the visual characteristics, or a loss of brightness. Afurther disadvantage is that an increase in crater density anddimensions is connected with a lowering of the process speed. Often thepeak pulse power achievable with a conventional pulsed laser is notsufficient to increase the crater dimensions.

SUMMARY OF THE INVENTION

Thus, the object of the invention is to propose a method ofmanufacturing non-slip floor coverings. with the aid of which method anincrease in the anti-slip effect can be achieved without there being anydisadvantageous impairment of the typical surface characteristics on theone hand and without any lowering of the process speed occurring, and inwhich, moreover, all the advantages of the laser structuring over othermethods of providing an anti-slip surface are retained.

According to the invention, this object is achieved with a method asdisclosed hereafter.

It is essential here that the non-slip floor covering, obtained in knownfashion as per DE 195 18 270 or WO 96/36469 is subjected to continuoushydromechanical aftertreatment. This hydromechanical aftertreatment canpreferably take place in the same installation directly following thelaser treatment and retaining the same process speed, whereby the wholeprocess, which comprises two process stages (laser treatment andhydromechanical aftertreatment), can be carried out continuously.

In certain cases however, e.g. when laser-treated floor coverings onlyreceive the hydromechanical aftertreatment at the place of installation,it can also be propitious for the two process stages to run separately,i.e. not continuously.

Advantageous developments of this whole process are representedhereinafter.

In accordance with the method according to the invention, thelaser-treated surface of the floor coverings or slabs conveyedhorizontally are briefly sprayed at least once with an acid, preferablyslightly acid, liquid during the continuous advance of the slabs.

After each of these spraying operations, the spray liquid is preferablydistributed by means of brushes or a wiper blade evenly on the surfaceof the floor coverings or slags and superfluous spray liquid is removed.

This even distribution preferably comes about in such a way that thespray liquid only remains in the depressions and in the microcratersproduced by the laser treatment, but not on the polished surface of thefloor coverings or slabs. Here the dosage of the liquid is chosen to bean amount corresponding approximately to the volume of the depressionsand microcraters.

As a result of the effect of the laser, the surface of the craters ismicroscopically very rough and thus very large in relation to the volumeof the craters. This produces very good conditions in which the diluteacid can work in the craters produced by the laser treatment and in themicropores which, depending on the type of slab, are present despite thepolish. The pH-value and the reaction time of the substantially dilutedacids by comparison with the chemical engineering treatment of floorcoverings are selected according to the invention to be such that thepolished surface is not impaired yet, inside the craters, because of thegood reaction conditions, parts of the surface are etched and thus thereis an increase in volume. By preference, those craters which are locatedin the region of the feldspar portions of the natural stone or finestoneware slabs are enlarged.

It is important to mention at this point that the reaction of time ofthe acid spray liquid depends on many factors, especially

the process speed

the distance between the first and the last of the spraying operationsserving to cleanse the surface from any preceding spray operations and

the concentration of the acid.

What is important is that the acid, which in individual types ofapplication can also be concentrated, only affects the depressions andmicrocraters without any impairment of the rest of the polished surface.

After the hydromechanical processing and the subsequent short (lastingpreferably between 60 and 150 s) reaction time of the acid in thecraters, the slabs are then sprayed again with a liquid, here at thehighest possible pressure, and brushed once more. Corresponding to thepH-value of the first liquid, the liquid to neutralise completely can bewater or also slightly basic (for example diluted lye).

In this connection, an advantageous development can consist of the factthat the pH-value of the liquid running off can be determinedcontinuously and this value used as the regulating variable for thepH-value of the spray liquid.

Through the mechanically stronger effect of the brushes in relation tothe distribution of the acid, residues which no longer belong to theparticle bond of the mineral components of the floor slabs and whichwould otherwise lead to a decrease in the possible crater volume, areremoved from the craters at the same time.

After the washing or neutralisation process, the slabs are dried withhot air.

The big advantage of the method according to the invention consists infact that, using this method, the advantages of the laser-structuredfloor coverings and slabs are preserved and the anti-slip effect isnoticeably increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a process line for the manufacturing of anon-slip floor covering accorded to the present invention; and

FIG. 2 is a schematic view of an alternative process line for themanufacturing of a non-slip floor covering.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is to be explained in greater detail via the followingembodiments, given by way of example.

Embodiment 1

The method variant as per embodiment 1 is sketched in FIG. 1. Deliveredfloor slabs, made of fine stoneware and equipped with an anti-slipfinish by means of pulsed laser bombardment and measuring 60×60×1.5 cm,are subjected in an installation to aftertreatment as per the methodaccording to the invention. The slabs 1 are here moved on a conveyorbelt 2 at a relatively high speed of 3 m/min. A liquid 4 containingdiluted hydrofluoric acid, with an acid concentration of 50% of themaximum possible, is applied to a polished slab surface 5 with themicrocraters 6 by a spray beam 3 via a 58 cm wide row of hole-typenozzles. At a spacing of 10 cm in the running direction of the slabsbehind the spray beam, there is located a rotating brush 7 with softbristles. The rotating brush 7 distributes the liquid 4 evenly into themicrocraters 6 and into the natural depressions of the slab 1 andsimultaneously removes superfluous acid from the surface 5. At a spacingof 50 cm from the spray beam 1, there is located a second spray beam 8which applies to the slab surface 5 a diluted lye 9 corresponding to theconcentration of the acid used, in order to neutralise it. In analogousfashion to spray beam 3, there is also located behind spray beam 8 arotating brush 10, which, however, runs at a higher rotational speed andhas greater contact pressure. Thus, in addition to the distribution andintensification of the neutralisation of the spray liquid 4, there issimultaneous removal of the liquids from the depressions and from theslab surface. Directly behind the brush 10, the slabs 1 run obliquelyupwards at an angle of 30°, and a jet of compressed air 11 is directedat the slab surface from a slot-type nozzle 12, against the direction ofmovement, at an angle of 30° to the slab surface, this air jet removingany remaining liquid residue both from the surface 5 and from themicrocraters 6 and other depressions. Thereafter, the slabs are dried(e.g. removal of the remaining moisture from the possible pore spaces)by one or more hot-air appliances 13 and the slabs 1 are conveyedonwards, e.g. to a packing station.

Embodiment 2

The method variant as per embodiment 2 is sketched in FIG. 2. From awork station 14 at which the anti-slip finish is applied through thetargeted production of microcraters 6 by means of pulsed laserbombardment, the laser-treated granite slabs 1, measuring 30×30×1 cm andin 2 rows beside one another, i.e., with a total width of 60 cm, passcontinuously on a conveyor belt 20 to the aftertreatment section 21. Therate of feed of the slabs 1, technologically determined by the lasertreatments, amounts to 0.6 m/min. Before the drying section 16, theslabs 1 first of all pass underneath a spray beam 3, which is againequipped with a 58 cm wide row of hole-type nozzles, however the nozzleholes are smaller in diameter than those of example 1 by a factor of 5.Here a liquid 4 containing diluted hydrofluoric acid, with an acidconcentration of 10% of the maximum possible, is sprayed on to thepolished slab surface 5 with the microcraters and the naturaldepressions 6. The total amount of the liquid 4 sprayed on is onlyapproximately 15% greater than the volume of the already existingcraters and depressions. At a spacing of approx. 15 cm in the runningdirection behind the spray beam 3, there is located a rotating brush 7with soft bristles. The brush axis is in this case disposed at an angleof 80° to the forward feed device. The rotating brush distributes theliquid 4 evenly into the microcraters and natural depressions 6 andremoves the superfluous liquid from the surface. At a spacing of, inthis case, 1 meter from spray beam 3, there is located an additionalspray beam 8, which sprays on to the slab surface 5 a lye 9 dilutedcorresponding to the concentration of the acid used and the sprayed-onamount, higher than the acid by a factor of 10. Directly behind thespray beam 8, there is located, here too, a rotating brush 10, in ananalogous arrangement to 7. Said brush is equipped with harder bristles,runs at a rotational speed ten times higher than that of brush 7 and ispressed harder against the slab surface. Spray beam 8 and brush 10 aremounted on a common device 24 the distance between which the spray beam3 can be adjusted. This is required at a given process speed in order tovary the necessary reaction time corresponding to the desired degree ofintensification of the anti-slip finish and taking into considerationdifferent slab materials. Following the last spraying and brushingprocesses, another spraying operation takes place with water beingsprayed from a slot-type nozzle 15 with a volume flow of 10 1/min on tothe slab surface 5. What is achieved by this is that possible remains ofthe already neutral mixture of liquids 9 and 4 and any possible lastremains of mechanical contamination and residue are completely removedfrom the slab surface 5 and from the microcraters and depressions 6.Thereafter, the slabs run through a drying section 16, where the slabsare dried by having warm air from hot-air appliances 17 blown on to themand by infrared irradiation 18. Between the working area of the brush 10and the slot-type nozzle 15, and between the slot-type nozzle 15 and thedrying section 16, there are located in each case plastic wiper blades19 which act as wipers for the liquids.

It is obvious that in each case after the individual wet sections (1stand 2nd spraying and brushing process, spraying operation) the liquidsare collected separately and subjected to aftertreatment, and after thecorresponding preparation are led again into the circulation or thewaste water removal system.

What is claimed is:
 1. Method for manufacturing non-slip floor coveringsor floor slabs, the non-slip floor coverings or slabs made of mineralmaterials having depressions in a 2-stage process by means of pulsedlaser bombardment, there being produced, statistically distributed, onthe surface of the floor covering, through the targeted action of laserpulses, microcraters acting like suction cups which are invisible to thehuman eye, characterized in that, in a second process stage, the surfaceof the laser-structured floor coverings or slabs so produced issubjected to purposeful hydromechanical post-treatment, it beingrepresented that the hydromechanical post-treatment comes about in sucha way that the surface of the laser-structured floor coverings or slabsis sprayed with liquid at least twice providing at least two sprayingoperations, at least one spraying operation serving to etch parts of thesurface of the microcraters and thus enlarge same, and wherein of the atleast two spraying operations, the last spraying operation serves to atleast one of clean and neutralise the surface of the floor coverings orslabs from previous spray liquids.
 2. Method according to claim 1,characterised in that the hydromechanical post-treatment is only carriedout in the depressions of the floor coverings or floor slabs.
 3. Methodaccording to claim 2, characterised in that the hydromechanicalpost-treatment is only carried out in the microcraters produced by meansof laser pulses.
 4. Method according to claim 1, characterized in thatafter each spraying operation at least one process takes place in whichthe spray liquid is evenly distributed on the surface of the floorcoverings or floor slabs and excess spray liquid is removed from thissurface, and finally at least one drying process is carried out. 5.Method according to claim 1, characterized in that the hydromechanicalpost-treatment happens in such a way that the surface of the floorcoverings or slabs is sprayed twice with liquids, the second sprayingoperation serving to one of cleanse and neutralize the surface of one ofthe floor coverings and slabs from the first spray liquid, after each ofthe first and the second spraying operations a process taking place inwhich the spray liquid is distributed evenly on the surface of the floorcoverings or slabs and excess spray liquid is removed from this surface,and finally at least one drying process being carried out.
 6. Methodaccording to claim 1, characterized in that, in one or more of thespraying operations serving to etch and thus enlarge the surface of themicrocraters, an acid is used as the spray liquid.
 7. Method accordingto claim 6, characterised in that an inorganic acid is used as the acid.8. Method according to claim 7, characterised in that a halogen hydracidis used as the acid.
 9. Method according to claim 8, characterised inthat hydrofluoric acid (HF-acid) is used as the acid.
 10. Methodaccording to claim 7, characterized in that the acid used is a diluteacid.
 11. Method according to claim 10, characterised in that the acidused is in an aqueous solution with a concentration of a maximum of 50%of its maximum concentration in water.
 12. Method according to claim 11,characterised in that the acid used is in an aqueous solution with aconcentration of a maximum of 10% of its maximum concentration in water.13. Method according to claim 1, characterised in that the spray liquidof the last spraying operation is neutral or basic.
 14. Method accordingto claim 13, characterised in that the pH-value of the spray liquid ofthe last spraying operation is a maximum of pH
 9. 15. Method accordingto claim 14, characterised in that the spray liquid of the last sprayingoperation is water (pH-value=7), the amount of water used being greaterthan the amount of spray liquid in the immediately preceding sprayingprocess.
 16. Method according to claim 1, characterized in that, afterthe last spraying operation, a process is carried out with the aid ofwhich the spray liquid of the last spraying process is removed from thesurface, the depressions and the microcraters of the surface of thefloor coverings or slabs, without leaving any residue.
 17. Methodaccording to claim 16, characterized in that the spray liquid of thelast spraying operation is removed from the surface of the floorcoverings or slabs by means of a jet of gas.
 18. Method according toclaim 4, characterized in that, with the exception of the last sprayingoperation, the process of evenly distributing the respective sprayliquid on the surface of the floor coverings or slabs is carried out insuch a way that the respective spray liquid remains only in thedepressions or microcraters, not however on the rest of the surface. 19.Method according to claim 18, characterised in that, with the exceptionof the last spraying operation, the distribution of the respective sprayliquid and the removal of the surplus spray liquid takes place by meansof at least one of a brushing process and a doctor blade.
 20. Methodaccording to claim 4, characterized in that the spray liquid iscompletely removed from the polished surface of the floor coverings orslabs and the depressions and microcraters.
 21. Method according toclaim 20, characterised in that even distribution takes place by meansof a brushing process.
 22. Method according to claim 4, characterized inthat the final drying takes place by means of hot-air appliances. 23.Method according to claim 22, characterised in that the drying takesplace by means of hot-air appliances fed with the warmed and filteredexhaust air and from infrared irradiation.
 24. Method according to claim1, characterized in that the whole method in the first and secondprocess stages can be carried out continuously in one installation, inthis case the speed of the passage of the floor coverings or slabsthrough the whole process, including the reaction times of therespective spray liquids on the floor coverings or slabs, beingdetermined by the speed of the first process stage (laser treatment),and in that, with the exception of the last spraying operation, strongundiluted acids are used as the spray liquid, and the spray liquid ofthe last spraying operation is adapted to neutralize the surface of thefloor coverings or floor slabs.
 25. Method according to claim 1,characterized in that the pH-value of the liquid flowing out of the lastspraying operation is measured and is used as the regulating variablefor the basicity of the last spray liquid.
 26. Method according to claim1, wherein a pH value is continuously determined of the first of the atleast two spraying operation for regulating a pH value of the sprayliquid of the last spraying operation.
 27. In a method for themanufacturing of non-slip floor coverings or floor slabs, the non-slipfloor coverings or slabs made of mineral materials having depressions ina two-stage process including the steps of bombarding the floorcoverings or floor slabs with a pulsed laser, forming and statisticallydistributing microcraters on the surface of the floor coverings or floorslabs through the targeted action of laser pulses, the microcratersacting like suction cups, invisible to the human eye, to formlaser-structured floor coverings or slabs, the improvement comprisingthe steps of: in a second process stage, subjecting the surface of thelaser-structured floor coverings or floor slabs to purposeful hydromechanical post-treatment, spraying the laser-structured floor coveringwith liquid, providing at least two spraying operations, spraying thelaser-structured floor coverings or slabs for etching parts of thesurface of the microcraters and thus enlarging the microcraters, andproviding a last spraying operation for at least one of cleaning andneutralizing the surface of the floor coverings or slabs from previousspray liquids.
 28. The improvement of claim 26, wherein thehydromechanical post-treatment is only carried out in depressions of thefloor coverings or floor slabs.